Abstract

Background

The predictive value of the psychosocial constructs of Theory of Planned Behaviour
(TPB) on subsequent dietary habits has not been previously investigated in a multivariate
approach that includes demographic factors and past dietary behaviour among adults.
The aim of this study was to investigate to what extent TPB constructs, including
intention, attitudes, subjective norms, perceived behavioural control, and perceived
social norms, measured at age 25 predicted four eating behaviours (intake of fruits
and vegetables, whole grains, total fat and added sugar) eight years later.

Methods

Two hundred and forty men and 279 women that participated in the Oslo Youth Study
were followed from 1991 to 1999 (mean age 25 and 33 years, respectively). Questionnaires
at baseline (1991) included the constructs of the TPB and dietary habits, and at follow-up
(1999) questionnaires included demographic factors and diet. For the assessment of
diet, a food frequency questionnaire (FFQ) with a few food items was used at baseline
while an extensive semi-quantitative FFQ was used at follow-up.

Results

Among men, attitudes, subjective norms and previous eating behaviour were significant
predictors of fruit and vegetable intake, while education and past eating behaviour
were predictive of whole grain intake in multivariate analyses predicting dietary
intake at follow-up. For women, perceived behavioural control, perceived social norms
and past behaviour were predictive of fruit and vegetable intake, while subjective
norms, education and past eating behaviour were predictive of whole grain intake.
For total fat intake, intention was predictive for men and perceived behavioural control
for women. Household income and past consumption of sugar-rich foods were significant
predictors of added sugar intake among men, while past intake of sugar-rich foods
was a significant predictor of added sugar intake among women.

Conclusion

After adjusting for potential confounding factors, all psychosocial factors assessed
among young adults appeared predictive of one or more eating behaviours reported eight
years later. Results point to the influence of psychosocial factors on future eating
behaviours and the potential for interventions targeting such factors.